Manufacture of blue-print sheets



April 18, 1939.

UNDER COAT.

W. M. HINMAN ET AL Filed March 8, 1937 TOP COAT.

CONTAINING SALT FROM GROUP: SOLUBLE FERRICYANIDE AND FERROCYANIDE SALTS;AND OPTIONAL CONTENTS OF SIMPLE OXALATE SALT AND BODY LIKE CONTAININGLIGHT-SENSITIVE FERRIOXALATE SALT AND SOLUBLE FERRICYANIDE SALT; ANDOPTIONAL CONTENTS OF REDUCING AGENT LIKE OXALATE SALT AND A BODY LIKEGELATINE.

GELATINE CARRIER LIKE PAPER fflyeizars. Zfla/fi'er" J6 flaw/mm PatentedApr. I8, 1939 UNITED STATES PATENT OFFICE.

2,154,506 mum-Acme or nrLUn-rnm'r sans-rs Walker M. Hinman, Winnetka.and Walter G. Hollmann, Chicago, Ill., assignors to The Frederlck PostCompany, Chicago, Ill., a corporation of Illinois Application March a,1937, Serial No. 129,040

Claims.

The present invention relates to blue print papers and the like of thetype in which light is used to produce a blue background of complex ironcyanogen compounds from appropriate 3 light-sensitive chemicalmixtures,followed by a the increase in the speed of printing a paper withoutsacrifice of depth of blue color, and

15 another aspect of the same problem, an increase in the depth of colorof a given speed" of paper. Attempts to solve these problems byincreased concentrations of sensitizing solutions and increasedthicknesses of sensitive coatings have reached a limited success, andthen other dlfiiculties are encountered.

The object of the present invention is to make a sensitizedblue-printing sheet which has when developed an improved depth of blueat a given printing speed, or a speedier paper for a desired depth ofblue.

A particular object of the invention'is to use initially in thesensitive coating a product which is formed ordinarily inthelight-printing operation.

Still another object 'of the invention is to thicken the coating bydividing it into two different but contiguous bodies or layers, and touse in one body or layer materials which need not be struck by light,while reserving for the other body or layer, materials which must bestruck by light.

Various other and ancillary objects and advantages of the invention willbecome apparent invention and of several ways of carrying it out.

The invention can best be understood by a brief reference to thefundamental chemistry of blue-print papers. Blue-print papers are. dry

ferrioxalate salt and potassium ferricyanide. The principle of operationholds that on exposing the sensitized paper to light the ferrioxalatesalt is reduced forming ferrous oxalate. This 50 is an insolublecompound which is fixed inp'osition in the paper and forms the patternof the print, and is changed later in situ to an insoluble bluecompound. In the presence of water the ferrous oxalate and the potassiumferri- 55 cyanide react to form insoluble blue ferrous from thefollowing detailed explanation of the sensitized sheets usuallycontaining a suitable ferricyanide. Where light does not strike thesheet the ferrioxaiate remains unchanged and the original unchangedsensitizing mixture is washed out. Thus the developed sheet contains nochemical where it is protected from light, and contains blueinsolubleferrous ferricyanide where it is struck by light.

Howeven'the practical operations are not fully in accordance with thismain principle, partly because there are side or additional reactions.The first of these is a minor chemical reduction which takes place,principally during exposure, by action of the oxalate content of thecoating on the ferricyanide, forming some theoretically undesiredpotassium ferrocyanide in the lightstruckportion, and leaving a portionof the theoretically desirable unchanged potassium ferricyanida.Therefore on wetting the exposed print there follows another sidereaction whereby the newly formed ferrous oxalate combines also with thenewlyformed potassium ferrocyanide to form ferrous ferrocyanide, whichis a white insoluble compound. It is thus seen that where theory callsfor transformation of the insoluble ferrous oxalate to a blue pigment, awhite pigment also may be formed by the secondary reaction. Mixturesfrom blue to white may result. If the exposure to light is weak, thesecondary reaction is .less and more blue pigment forms. If the exposureto light is strong the secondary reaction is greater and muchmore whitepigment forms. In commercial practice there are mixed white and bluepigments having a a greyish blue appearance at this stage' In fact, it,is a practice to encourage the photochemical reduction of ferricyanidesalt to ferrocyanide salt by having present additional reducing agentsuch as an oxalate, a citrate or a tartrate; but preferably an excess ofsome soluble oxalate salt.

Theory at this stage calls for complete washing out of soluble material,largely solubleoxalate salts, so as to leave only these mixed white andblue pigments. Then, practice calls for oxidation whereby the insolublewhite ferrous ferrocyanide is converted to insoluble blue ferricferrocyanide. Air will oxidize it, but this is too slow. Hence achemical oxidizer is used, and such use in more perfected form is setforth in the copending. application of applicant Hinman, Serial No.727,248, filed May 24, 1934, the inventionof which is applicable to thepaper made by the present invention.

Referring'to .the above description, it should be stated that itdescribes what occurs in blueprint papers having a sensitizing mixtureof ferrioxalate and ferricyanide as appropriate salts. The ferrioxalateis essentially the one compound which must be decomposed or altered bylight to produce ferrous oxalate. At the same time the ferricyanide isonly incidentally but desir-' ably altered, and that occurs because itis usually present with some form of reducing agent, usually theferrioxalate or other oxalate, which furnishes the reducing powerwhereby a ferro cyanide is formed. But this incidental reductionutilizes some of the actinic energy which should be directed towardforming ferrous oxalate; As

a result the paper is slower printing for a given depth of blue, or elsethe blue is weaker for a given time of printing.

According to the present invention this incidental waste of actinicenergy in the light-printing period is minimized. The manner in whichthis is done may be presented in several aspects, but generally it maybe said that the essential light-sensitive ferrioxalate is moreeffectively concentrated near the surface of the sensitizedsheet, andthe ferricyanide content which ordinarily goes with it is lessened. Notonly is this accompanying ferricyanide content, lessened by shifting itslocation, but the shifted portion is in whole or in part replaced byferrocyanide and located below the top surface but contiguous thereto.

And in addition, to maintain more or less distinct but contiguous bodiesor layers, a sizing, or matrix, or body, or vehicular substance 'ofsuitable sort may be used in one or both bodies or layers, to maintain acertain degree of isolation, at least until after the light-exposure hasbeen made.

Thus, it has been found that more of the light energyin printing may beused to form a deeper field or image of insoluble ferrous oxalate. Upondevelopment by wetting, the chemicals of the inner and outer layersreadily diffuse to meet with each other. Thus the insoluble ferrousoxalate' formsthe blue insoluble ferrous ferricysnide, and also formsthe white insoluble ferrous ferrocyanide, which latter is oxidizable indevelopment to insoluble blue ferric ferrocyanide.

At this point it is pertinent to state that a dried I paper coated onlywith a solution of ammonium speed.".

In the practice of the present invention it has been found that theprior art practice of having ferrioxalate and ferricyanide intimatelyassociated, must still beobservedmnd the ratio of these may vary greatlyas in the prior art. .It has not been found possible to make a completeseparation as the general discussion might lead the reader up to thispoint to suspect. Hence, since ferricyanide must be used in the surfacecoat, body or layer, it is preferred to use in the lower coat, body orlayer ferrocyanide without ferri- 'cyanide, and to reduce theferricyanide content of the surface coat, body or layer. In practicethetotal quantity of iron cyanides thus employed in both bodies orlayersmaybe'less thanhas in place in developing the sheet.

been needed heretofore when there has been no separation into twoportions.

In creating the coats, bodies or layers it becomes necessary to usesomething to define the same and to maintain some line of demarcationbetween them. This may be accomplished simply by using a gum or colloid.or other coating substance which will contain the chemicals, and whichwhen wet will permit .the release or the difiusion of such chemicalsfrom the colloid. Many film-forming substances are known and may be usedsuch as: glue, gelatine, starch, dextrine, oxidized starch, otherconverted or soluble starches and starch derivatives, certain cellulosederivatives, regenerated cellulose, gum .arabic,

gum tragacanth, and a large number of gums and substances which maygenerally bedesignated as hydrophilic colloids or substances. Preferablythey are used in solution form and are dried after application. Ofcourse a paper'base itself may constitute a medium to define the firstresidue, and a second residue may be formed thereon. But usually thepaper base for blue-print papers is highly sized or finished so that itssurface is not at all or not very absorptive of coating solutions, thusto form more nearly true coatings rather than impregnated papersurfaces. It is customary in the ordinary coating of blue-print paper touse a coating solution containing an agent of the character abovespecified, such as glue or 'gelatine, partly in order to facilitatespreading of the sensitizing composition with even distribution over thesheet, and to hold it The present invention therefore contemplates usingsuch agent in either or in both compositions to be applied in creatingbodies or layers. It is also to be considered that a body or layer maybe formed in two operations as well as in one, by first applying asuitable asent such as gelatine, or even regenerated cellulose, whichmay be dried in whole or in part, and then wetted with a solution whichmay contain the chemicals and may be lacking in a glue-like substance. I

In practical operations under this invention a well sized paper is used.This is coated with an under-coating composition containing hydrophilicsubstance and certain chemicals, and then dried. The driedcoating may becovered immediately or later with the surface-coating composition. andthis likewise contains hydrophilic body substance by preference and thelight-sensitive chemicals. If the hydrophilic body is omitted and thecoating composition contains only chemicals, these enter the surface ofthe socalled-dried under-coating to a degree, but yet contiguoussuperimposed coats are present, although not sharply defined. Bypreference therefore, an agent such as selatine is included ineachcoating composition to maintain more eomplete-separation. Also, itis preferred to dry the first coating and to coat immediately, to formthe second coating, since this assures uniform surface conditions on theundercoat for receiving the second coat, whereby the dual coatingspresent a uniform product when continuous production is employed.Actually, one drying oven is employed for a continuous web of paper.There aretwo' coating baths and devices, one positioned drying oven. Anoven temperature of I".

is suitable for all the-solutions hereinafter .dis-

closed, but it is to be understood that this tem-' perature is notcritical, nor is heat necessary for the process. Ordinary coatingdevices known to the art suflice for each coating composition.

Exmu: I

Under coat. Water to gallons 1 Pounds Sodium ferrocyanide 1 Ammoniumoxalate 32 Potassium ferricyanidm 6 Powdered glue (adhesive grade) 26Surface coat. Water to 100 gallons Pounds Ammonium ferrioxalate Ammoniumoxalate 32' Potassium ferricyanide 18 Exmnn II Under coat. Water to 100gallons Pounds Potassium ferrocyanide 6 Ammonium oxalate 32 Gelatin 6.5Surface coat. Water to 100 gallons 1 Pounds Ammonium ferrioxaiate 175Ammonium oxalate 8 Potassium ferricyanide 18 Gelatin 0.5

Under coat. Water to 100 gallons Pounds Sodium ferrocyanide 6.00 Oxalicacid 31.25 onia (26 Be.) 16.25 Anhydrous potassium carbonate.- 12.00Powdered glue 14.25 Monosodium phosphate 3.50

Surface coat. Water to 100 gallmts Ammonium ferrioxalate lbs 189 Ammonia(26 es.) do 7.38 lvionosodium phosphate do 8.25 Qxalicacid do 7.00Photoengraving glue ml 630 Potassium ferricyanide lbs 23.25

under the influence of light. The mono-sodium phosphate has also aretarding function, but doubtlessly through the difierent mechanism ofhydrogen ion control by its bufier action. In Examples I and II theoxalate salts are employed as such in compounding the formula, and theammonium salt alone is'used', since it is fairly insoluble and does notso readily transfer from the dried under coat in applying the surfacecoating composition. lmExample 111 these oxalate salts are built up fromformative components, such as oxalic acid,.ammonia, and potassiumcarbonate, forming both ammonium oxalate and potassium oxalate. Slightexcess of any such component is not harmful in the presence of thebufier salt monosodium phosphate, and this gives some latitude forvariations of the formula by carelessness, error, or variations inmaterial.

The accompanying drawing illustrates the invention showing particularlythe arrangement of the bodies. In the drawing III illustrates thecarrier base, which is preferably a well-sized sheet of paper ascommonly used in the blueprint field, which can receive a liquid coatingcomposition and form a residual coat when dried. Numeral ll representsthe position of the resulting dried coat, as may be readily producedfrom the solutions designated Under coat in the examples. Numeral 12represents the position of the residue formed by coating onto the drybody ii a composition such as that designated Surface coat in theexamples, and drying the'same; The

legends on the parts indicate briefly the variations discussedhereinabove.

Returning to. the pertinent phases of the invention it may be noted thatsome of the oxalate content of the prior art, as well as some of theiron cyanide content, has been transferred from the light-sensitivesurface coat I! to the undercoat ll. Since some reducing agent inaddition to the oxalate content of ferrioxalate is desirable fortransforming ferricyanide to ferrocyanide, it is desirable not to moveall of the oxalate or other reducing agent (citrates and tartrates beingalso used), into the under coat. However, the lessened concentrations ofsuch reducing agent and of ferricyanide salt is efiective to lessen thetendency for the ferricyanide to use up actinic energy in being reducedto ferrocyanide. Thus there is left a greater opportunity for thepreponderating quantity of ferrioxalate to be reduced to thefleld-image-forming ferrous oxalate, without collateral loss caused bythe presence of chemicals necessary for the later reactions ofdevelopment.

From the foregoing it will be readily understood how the invention maybe modified and changed from the preferred exples given. It isappreciated that difierent manufacturers of blue-print papers usevariations of many basic formulas, and employ difierent combinations ofpotassium and ammonium salts. All those de perturesand modificationsnaturally occurring to those skilled in the art, and suggested herein.

sheet having two contiguous water permeable coats containing chemicalingredients, one coat being light-sensitive and located for positioningit between the other and a source of 'actinic light and containinglight-sensitive ferrloxalate salt,

a soluble ferricyanide salt and a reducing agent therefor capable ofconverting the ferricyanide to ferrocyanide by the action of actiniclight,-and the other coat containing a soluble complex salt of the groupconsisting of ferricyanide and ferrocyanide-which is adapted to difluseto the first coat upon wetting for reaction with the insoluble ferrousoxalate formed in the light-sensitive coat by the action of light.

. 2. A sensitized blue-print sheet comprising a sheet having twocontiguous water-permeable various salts, usually selecting from sodiumfcoats containing chemical ingredients, one coat being light-sensitiveand located for positioning it between the other and a source of actiniclight and containing light-sensitive ferrioxalate salt, I. a solubleferricyanide salt and a reducing agent therefor capableof converting thefen'icyanide to ferrocyanide by the action of actinic light, and theother coat containing a soluble ferrocyanide salt which is adapted todiffuse to the first coat 1. upon wetting for reaction with theinsoluble ferrous oxalate formed in the light-sensitive coat by theaction of light.

3. A sensitized blue-print sheet comprising a sheet having twocontiguous water-permeable 1 coats containing chemical ingredients, onecoat therefor capable of convertingtthe ferricyanide to ferrocyanide bythe action of actinic light, and the other coat, containing ,a solubleferrocyanide salt and a soluble fer'ricyanide salt both of which areadapted to diffuse to the first coat upon wetting for reaction with theinsoluble ferrous oxalate formed in the light-sensitive action of light.L A sensitized blue-print'sheet comprising a sheet having two contiguouswater-permeable coats containing chemical ingredients, one coat beinglight-sensitive and located for positioning it between the other and asource of actinic light and containing light-sensitive ferrioiutlatesalt, a soluble ferricyanide salt and a reducing agent therefor capableof converting the ferricyanide to ferrocyanide by the action of actiniclight, and the other cost containing a soluble oxalate salt, and also asoluble ferrocyanide salt and a soluble fen'icyanidesaltboth of whichare adapted to difiuse to the first coat upon wetting for reaction withthe insoluble ferrous oxalate formed in the light-sensitive coat by theaction of light.

5. A sensitized blue-print sheet comprising a sheet having twocontiguous water-permeable coats containing chemical ingredients, onecoat being light-sensitive and located for positioning it between theother and a source of actinic light and containing light-sensitiveferrioxalate salt and a soluble fen'iiiyanide salt as the essentialingredients for reaction under the influence of actinic light to produceinsoluble ferrous oxalate,

being 'light -sensitive and located for positioning; 4 it betweenthe'other and a source of actinic light and containing light-sensitiveferrioxalate. salt,

and asoluble ferricyanide salt as the essential ingredients for reactionunder'the influence of and the other coat containing a supply of solublesalt of the group consisting of ferricyanideand ferrocyanide essentialforthe development of. an insoluble pigmert upon application of water,by diffusion torand reaction with the ferrous oxalate,

"each of said coats being more or less definite and containing a body ofhydrophilic substance housing the respective chemical ingredients,

7. A light-sensitive sheet for blue-printing I. I comprising alight-sensitive material in extended coat by the actinic light toproduce insoluble ferrous oxalate,

. of light and containing essentially a light-sensitive mixture ofsoluble salts-of ferrioxalate and ferricyanide, and contiguous materialin like form positioned in .the sheet to be more remote from saidsource. of actinic light than said first form, said second formcontaining a soluble ferrocyanide salt, both materials being permeableto water to cause difiusion of ferrocyanide from thesecond form to thefirst form for development of a light-exposed print.

8. A sensitized blue-print body comprising a carrier base having twocontiguous water-permeable layers thereon containing chemicalingredients, one layer being light-sensitive and located for positioningit between the other and a source of actinic light and containinglight-sensitive ferrioxalate salt, a soluble ferricyanide salt and areducing agent therefor-capable of converting the ferricyanide toferrocyanide by the action of actinic light, and the other layercontaining a soluble complex salt of the group" consisting offerricyanide and ferrocyanide which is adapted to diffuse to the firstlayer upon wetting for reaction with the insoluble ferrous oxalateformed in the light-sensitive layer by the action of light.

9. A sensitized blue-print body comprising a carrier base'having twocontiguous water-permeable layers thereon containing chemicalingredients, one layerbeing light-sensitive and located for positioningit between the other and a source of, actinic light 'and containinglight-sensitive ferrioxalate salt, a soluble ferricyanide salt and areducing agent therefor capable of converting the ferricyanide toferrocyanide by the action oi actinic light, and the other layercontaining a soluble ferrocyanide salt and a soluble ferri cyanide saltboth of which are adapted to diffuse sensitive layer by the action oflight.

10. A sensitized blue-print body comprising a carrier base having twocontiguous water-permeable layers thereon containing chemicalingredients, one layer being lint-sensitive and located for positioningit between the other and a source of actinic light and containinglightsensitive ferrioxalate salt, and a soluble ferricyanide salt as theessential ingredients for re- 4 action under the influence of actiniclight to produce insoluble ferrous oxalate, and the other layercontaining a supply of soluble salt of the groupconsisting offerricyanide and ferrocyanide essential for the development of aninsoluble pigment upon application of water, by diffusion to andreaction with the ferrous oxalate, each of 'said layers being more orless definite and containing a body of hydraphilicsubstance housing therespective chemical ingredients.

'11. The process of making sensitized bodies for blue-prints of the typein which a lightsensitive ferrioxalate salt is altered by light toproduce insoluble ferrous oxalate and in which a soluble complex salt ofthe group consisting of 'ferricyanide and ferrocyanide unites with theferrous oxalate to form an insoluble complex iron iron-cyanide whenwater is'applled, the steps of coating a carrier body with an aqueouscoating composition containing salt from said abovementioned group.drying the application to a coat on said body, then applying to saidheat a second aqueous-coating composition carrying a light-sensitizingsubstance including essentially light-sensitive ferrloxalate salt, alesser quantity of soluble ferricyanide salt, and a reducing agent whichis capable of converting the last-mentioned ferricyanide salt to aierrocyanide salt by the action of actinic application to a coatoverlying the first coat. while preserving the light sensitive characterof the resultingoverlying coat.

12. The process of claim 11 in which the first coating compositionincludes a simple oxalate salt.

13. The process of claim 11 in which at least one of the coatingcompositions contains a dimiorming hydrophiiic substance as a bodydefining the resulting coat.

14. The process of making sensitized bodies for blue-prints of the typein which a light-sensitive terrioxalate salt is altered by light toproduce insoluble ferrous oxalate and in which a soluble complex salt ofthe group of ferricyanide and ferrocyanide unites with the ferrouslight, and drying said second 4 oxalate to form an insoluble cyanidewhen water is applied, the steps of coatin: a carrier body with anaqueous coating, composition containing salt from said above-mentionedgroup, drying the application to a coat on said body, then applying tosaid coat a second aqueous coating composition carrying alightsensitizing substance including essentially lightsensitiveierrioxalate salt and a. lesser quantity oi soluble ierrlcyanide salt,and drying said secand application to a coat overlying the first'coat.

while preserving the light-sensitive character of the resultingoverlying coat.

15. The process of claim 14 in. which at least one o! the coatingcompositions contains a dimiorming hydrophilic substance as abodydeflning the resulting coat.

- WALKER M.

complex iron ironmm. WALTER G. HOI..1MANH. v

